1. Field of Invention
The present invention relates to a light ray refraction element and an optical axis displacement device, and a projection display apparatus based on the light ray refraction element.
2. Technological Background
In recent years, there have been active developments of projection display devices which enlarge and display images on a light valve by means of an optical projection system. Especially, the use of transparent, active matrix liquid crystal display panels (referred to as TFT.LCD hereinbelow) as the light valve component in projection display devices (shortened to projectors hereinbelow) is gaining attention. This is because such panels provide excellent color reproduction and contrast, and provide simple apparatus for creating large screen images of impressive scale. The development of liquid crystal projector for high definition television (HDTV) applications has already been realized.
A conventional type of projector is schematically illustrated in FIG. 48. In this figure, the reference numeral 1 refers to a light source, 2 is a filter for filtering the infrared (IR) and ultraviolet (UV) components for the light generated from the light source 1, 3 is an optical filter, 4 is a condensor lens to condense the ray from the light source 1, 5 is a light valve, 6 is a projection lens and 7 is a screen.
Such a projector displays images, produced in the light valve 5 using the regular LCTV technique, on the screen 7 through the projection lens 6. In this system, the light valve 5 itself is not luminescent, and the image on the light valve 5 is illuminated from the back with the light source 1 and is enlarge by the projection lens 6.
To achieve higher image resolution with the above optical configuration, it is necessary to have a quantum increase in the density of pixels on the TFT.LCD so as to accommodate the huge increase in the screen display area. This approach requires that the bus line resistance in the LCD circuit be lowered, the density of pixels be increased and the TFT driving capability be improved; however, these requirements are difficult to be met in production, and the manufacturing yield suffers as a result. Further, LCD circuits of such a complexity demand higher circuit performance, such as faster driving LSI and other components. For this reason, the conventional approach to improving the image resolution has been to utilize a number of projectors to project several images of one image from different projectors so as to compensate for the vacant spaces between the pixels from different projectors. Examples are disclosed in a Japanese Patent Application, First Publication, S64-35479 and a Japanese Patent Application, First Publication, H2-281287.
An example of such a multi-projector system is shown in FIG. 49. In this figure, the reference numerals 11, 12 refer to light sources, 21, 22 are IR and UV filters respectively, 31, 32 are optical filters, 41, 42 are condensor lens, 51, 52 are light valves, 61, 62 are projection lenses, 7 is a screen, m1, m2 are optical axes of the projection lenses (i.e., projectors).
As illustrated in FIG. 49, the images on the light valve 51, 52 are interleaved on the screen 7 to form a composite image. The mechanism of such an interleaving projection system will be explained with reference to FIG. 50.
FIG. 50 illustrates a case of interleaving four component images (A, B, C and D) to produce a composite image E. The images A, B, C and D are formed on TFT.LCDs which constitute four individual light valves. A component image is formed by numerous pixels such as those shown by the four shapes in this figure, and a pixel consists of a light aperture portion for transmission of light and a light shield portion. It follows that by projecting a composite image by shifting a half pixel for each interleaved image such that each light aperture portion of one image overlaps with the light shield portion of the other images, it becomes possible to achieve a precision projection display which is twice the size of the original image.
To successfully project a high-resolution composite image by such a interleaving technique, it is necessary that every opening section of every pixel in the entire image align precisely with every light shield portion of all other pixels of the other images. This means that not only condensing of the images but other optical factors of the pixels such as the size, distortion and the rotational direction on the screen, should be identical for all the pixels. This means that the system requires adjustments in the direction of six axes, x, y z, .theta.x, .theta.y, and .theta.z, for each optical axis of a projector, as illustrated in FIG. 51.
In the conventional system, such adjustments are made with a precision optical stage for R & D, and such a stage had to be large and sturdy so as to accommodate a projector weighing several tens of kilograms, thus resulting in an extremely heavy stage.
Furthermore, since the stage is heavy, adjusting mechanisms such as stepping motors for driving the stage had to be correspondingly powerful, thus resulting in a giant overall projection system.